a source port is a new engine created from the games orginal source code usually with some modern improvements and improved renders some even add in online multiplayer. All you need is the game files in this case the .wad files and either place them in the location of the source port's .exe or place the .exe for the source port in the game's location and if you want to run it via steam just rename the source port .exe to Dosbox when placing it in doom 2 folder that way Steam loads that up instead of Dosbox.

If you would prefer the DOS version go My Computer and find your doom 2 directory the default is C:\Program Files\Steam\steamapps\common\Doom 2\base now load up the setup file in dosbox (drag file to dosbox icon) go to control setup and change it to your liking make sure to save hope this helped.

I actually found a control schme that I found very comfortableI disabled horizontal movement on the mouse so I can aim with the mouse and move with wasd and shoot with crtl and open doors with space ;)

The Steam release forgot to include the SETUP.EXE files used to configure settings with the vanilla DOS version of Doom. GOG's release of the Doom games thankfully didn't make this mistake or any other the Steam version made and neglected to fix.

The Steam release forgot to include the SETUP.EXE files used to configure settings with the vanilla DOS version of Doom. GOG's release of the Doom games thankfully didn't make this mistake or any other the Steam version made and neglected to fix.